As the web, and the technologies that drive it, have evolved, some of the early technologies that filled gaps are becoming obsolete. Internet Explorer used ActiveX to fill gaps with plugins like Flash and Silverlight. Modern browsers have already begun excluding these dated technologies as we approach the end of support life cycles. Modern, more secure, technology has moved in to take its place and end users need to prepare for the changes to come.
Here are the official statements of the respective companies:
Microsoft, on Silverlight 5, has announced the End of Life (EOL) through October 12, 2021, or the lifecycle of the underlying browsers, whichever is shorter. ( https://support.microsoft.com/en-us/help/4511036/silverlight-end-of-support )
Microsoft, on Internet Explorer 11, does not have an officially announced EOL date. They say they provide a minimum of five years of mainstream support, and an additional five of extended support for business. Internet Explorer 11 released Oct 17, 2013. This would imply that mainstream support ended Oct 17, 2018, and extended support would end Oct 17, 2023. Microsoft encourages the use of the Microsoft Edge browser and to limit use of IE11 to backwards compatibility only. ( https://support.microsoft.com/en-us/help/17454/lifecycle-faq-internet-explorer )
Adobe, on Adobe Flash, in collaboration with Apple, Facebook, Google, Microsoft, and Mozilla, is planning to EOL Flash. They intend to updating and distributing Flash Play at the end of 2020. They are encouraging content creators to migrate any existing Flash content to a new open format such as HTML5, WebGL, or WebAssembly. ( https://theblog.adobe.com/adobe-flash-update/ )
What does this mean to the end users?
End users should begin seeking alternatives to dated web applications that require Internet Explorer, Flash, or Silverlight to run. Once these products reach EOL they will no longer receive important security updates. This will ultimately lead to vulnerabilities on systems using these technologies.
End users who proactively move to modern browsers such as Microsoft Edge, Google Chrome, or Mozilla Firefox will be ahead of the change. However, they also need to find alternatives to dated technology or push to have those resources updated to modern open formats.